How cost effective will the Grasshopper really be?

[Themohawkninja]

To me, the Grasshopper rocket seems wasteful, because SpaceX (or any other future company that wishes to design a VTVL rocket design) could just utilize all of that extra fuel to get a bigger, better payload into orbit, so is it really worth soft landing a fuel tank (which brings up the other question of: "Why don't they just use parachutes?") by burning all of that rocket fuel? The Space Shuttle used two SRB's (which as I understand it, solid fuel is usually cheaper pound for pound than liquid fuel), and NASA had those parachuted to the ground after they decoupled, and it was still economically inefficient (they did it because of the bureaucracy).

[ajwojo1210]

I'm not sure if you know this but, the Grasshopper is not the actual vehicle that will make the soft landing after launching the payload. All it is doing is testing the procedures upon SpaceX will recover the Falcon 9 V1.1.

All of this aside, the reason why parachutes would not work is for one they have been tried on the earlier launches and it never worked. The first stage of the Falcon 9 is also grossly heavier than an SRB. Also when the SRB's hit the water they become filled with salt water, an extremely corrosive mixture which is costly to clean and repair. Another reason to have the ability to have a launch vehicle which can return softly to the launch site has been shown with the shuttle. A quick turnaround between launches becomes possible. That, in theory, should drop launch prices as time passes.

[Scotius]

First: Grasshoper is just a testbed and technology demostrator. No one intends to fly it into space.

Second: imagine this - you are flying somewhere on a plane. But when you reach your destination instead of landing normally, you are ditching your plane and landing using parachute. You could've saved a lot of fuel this way, right? No. Fuel is just a fraction of the cost of space vessel. Hardware is what most dough goes into, along with all maintenance it requires (which ain't cheap too). For most of the space age we've lacked the means (or maybe it was will) to bring our expensive rockets back, fix what needs fixing and put them back on the launchpad. SpaceX seems determined to finally overcome that hurdle - and i wish them best of luck, keep my fingers crossed and pray to any higher being that might be watching

[Fuzzy Dunlop]

Well the reason you don't use parachutes is because you want to land on the point back at base rather than splashing down at some random spot in the ocean. Landing at an exact location is just about the only thing the space shuttle got right. Finding and retrieving large rocket stages can become very expensive. Put it this way - the shuttle eneded up with a load of comercial divers on staff (to secure the underwater sections of the SRBs), these are not the kind of people you can afford if you are trying to build a low-cost launch system.

The other point is that it doesn't require that much fuel to land a rocket, the mass of the empty 1st stage is well under than 10% of the mass at launch. You only really need 1 of the engines running at low power to guide it gently to the ground.

All of this aside, the reason why parachutes would not work is for one they have been tried on the earlier launches and it never worked. The first stage of the Falcon 9 is also grossly heavier than an SRB..

Thats not true, the shuttle SRBs are made of 2" maraging steel, the Falcon 9 is made of the thinest aluminium alloy they can get away with. In fact it's doubtful that a Falcon 1st stage could survive the forces the SRBs undergo when they hit the water (which is another reason they don't really want to use parachutes).

It's worth noting that even after the SRBs were fished out of the sea they still had to be disassembled, shipped to Utah, overhauled, reloaded with propellent, (which is difficult dangerous and expensive), shipped back and put back together again. With a liquid booster all you should have to do is check it out and refuel it.

[ajwojo1210]

Thats not true, the shuttle SRBs are made of 2" maraging steel, the Falcon 9 is made of the thinest aluminium alloy they can get away with. In fact it's doubtful that a Falcon 1st stage could survive the forces the SRBs undergo when they hit the water (which is another reason they don't really want to use parachutes).

While that may be true, I imagine 9 Merlin engines are close or above the weight of 1 SRB. Now I may be wrong as that was just a guess.

[Eric S]

I remember reading something about this to the effect that the fuel it uses to land is the emergency reserve fuel that is already there in case something goes wrong (like an engine failure that reduces the total TWR, causing the craft to spend more delta-v fighting gravity). So basically, if nothing goes wrong, it uses the emergency reserve to land, if something does go wrong and the emergency reserve gets used, they lose that stage.

Remember, with no payload, most of the fuel gone, and atmospheric drag working in your favor instead of against you, it doesn't take that much fuel to land like this, at least not compared to launching.

[Fuzzy Dunlop]

While that may be true, I imagine 9 Merlin engines are close or above the weight of 1 SRB. Now I may be wrong as that was just a guess.

Well you're right that the engines are the heaviest part of the stage at about 7.7 tonnes, the whole thing having an empty weight of about 15 tonnes. But an empty space shuttle SRB is about 91 tonnes.

[ajwojo1210]

Well you're right that the engines are the heaviest part of the stage at about 7.7 tonnes, the whole thing having an empty weight of about 15 tonnes. But an empty space shuttle SRB is about 91 tonnes.

At least I was right about something. Hmmm Now that I think about it, an SRB seems like an extreme weight that KSP just doesn't simulate correctly

[AmpsterMan]

I think a nice, rough test would be to launch a payload in KSP, decouple the spent stage and try to land it back to base. while this would prove very little in reality, it might make a case for how much fuel is required to land. My guess would be that the required amount of fuel would be much less than one might think and, if done correctly, might reduce operating costs.

Furthermore it is a step to fully reusable space vehicles, which I believe to be a good thing.

[ThreeKelvin]

Also, the cheapest part of a rocket is the fuel. The rocket engine and the turbine pump are the horribly expensive parts, but even the tanks alone are more expensive than the fuel they store just in raw materials.

[Fuzzy Dunlop]

At least I was right about something. Hmmm Now that I think about it, an SRB seems like an extreme weight that KSP just doesn't simulate correctly

KSP is quite misleading because the liquid rocket engines have much less thrust to weight than real life; from memory a mainsail is about 25:1 whereas a Merlin D is more like 150:1. KSP needs this because otherwise every single rocket would be an SSTO, but it does cause a few anomalies compared to real life.

The space shuttle SRBs are absolute monsters, they each weigh something like 590 tonnes fully fueled, which put together is much more than the external tank and orbiter combined. They provide about 80% of the liftoff thrust. What KSP doesn't really model is how much power SRBs pack in a small (but very heavy) package.

[kujuman]

One way to visualize just how beefy the Shuttle SRBs are is to remember that they carry the entire weight of the launch vehicle before launch. It's nuts.

[NovaSilisko]

I believe the current estimate is that the first stage, not counting the fuel, makes up 70% of the total vehicle cost. If you can recover that first stage and use it immediately, that's 70% of the cost of a new vehicle you don't have to spend.

[Giggleplex777]

I believe the current estimate is that the first stage, not counting the fuel, makes up 70% of the total vehicle cost. If you can recover that first stage and use it immediately, that's 70% of the cost of a new vehicle you don't have to spend.

More like 65%. Refurbishing the first stage still costs a bit due to heat damage on the engines.

[stupid_chris]

One way to visualize just how beefy the Shuttle SRBs are is to remember that they carry the entire weight of the launch vehicle before launch. It's nuts.

No totally true, the shuttle's three launch engines are burning on liftoff too. Mainly, the SRBs are giving a boost to the TWR until the shuttle's engines burnthrough the fuel and gain enough TWR to fly on their own in the upper atmosphere.

[Fuzzy Dunlop]

No totally true, the shuttle's three launch engines are burning on liftoff too. Mainly, the SRBs are giving a boost to the TWR until the shuttle's engines burnthrough the fuel and gain enough TWR to fly on their own in the upper atmosphere.

He means before any engines are lit only the SRBs are connected to the pad, and they hold up the entire stack.

[stupid_chris]

He means before any engines are lit only the SRBs are connected to the pad, and they hold up the entire stack.

Oh, sorry my bad then

[Fuzzy Dunlop]

I was messing around with this in KSP tonight, as a challenge it varies from moderately difficult to utterly impossible. Landing isn't too hard (well it is but only because the high gravity of Kerbin punishes mistakes - my best attempt ended up landing, bouncing back up then slaming sideways into the VAB). The main issue is getting back to the KSC, which becomes very difficult if you're moving downrange fast enough. Also it's very hard to eyeball it, I once overshot KSC by at least 20 km.

[AmpsterMan]

I was messing around with this in KSP tonight, as a challenge it varies from moderately difficult to utterly impossible. Landing isn't too hard (well it is but only because the high gravity of Kerbin punishes mistakes - my best attempt ended up landing, bouncing back up then slaming sideways into the VAB). The main issue is getting back to the KSC, which becomes very difficult if you're moving downrange fast enough. Also it's very hard to eyeball it, I once overshot KSC by at least 20 km.

How much fuel did you need as a fraction?

[Nibb31]

How much fuel did you need as a fraction?

My Kerbal testing for returning a first stage launcher to the launch site needed something around 10 or 20% of the first stage propellant. Of course, that is meaningless, because mass fractions, distances, fuel density, launch profiles, ISP, consumption, etc... are all messed up in KSP, so real life figures would be totally different.

In real-life, there is a heavy penalty for reusing the first stage, due to:

- Extra mass for reinforcing the tank

- Extra mass for the landing gear

- Extra mass for the return trajectory and landing fuel

- A suboptimal launch trajectory

If you are recovering your first stage, you don't want an early gravity turn, because any horizontal speed will have to be reversed if you want to return to your launch site. You want a launch profile that remains as vertical as possible until the first stage runs out, so that it can come as straight down as possible, and let the second stage handle most of the horizontal speed. Of course, anyone who has played KSP knows that this is wasteful, and reduces your payload. It also means that you need a beefier second stage, which also eats into the payload mass.

So yes, a reusable Falcon 9R will have a massively reduced payload. I believe they are aiming for 7 tons to LEO instead of 11 tons. This puts the F9R in the same class as Soyuz or Ariane 6, whereas the non-reusable F9 1.1 is in the same class as Ariane 5, Delta IV or Atlas V. The plan is that the savings of reusing the first stage instead of building a new one allows for a lower price per pound to orbit. The jury is out on whether they can manage to be cheaper than Ariane 6 or Soyuz.

On the other hand, it can be argued that the best way to reduce hardware costs is mass production of cheap elements. That is the approach of Ariane 6: cheap mass produced SRBs as a first and second stage. While the Merlin engines are cheap and simple, reusability gets in the way of mass production by reducing the production rate and adding complexity to the elements (landing gear, avionics, weight, etc...). There is also the cost of refurbishing and testing, which is still unknown.

SpaceX seems to have done the math and figured that it works. We'll see. At least they are trying something new. But lets not forget that this isn't a holy grail, as Kryten posted this in another thread:

But there's another factor; spaceflight costs involve a heck of a lot more than launch. Satellite operators operate (very roughly) on the 'rule of fifths'; a fifth of the budget for the satellite bus, a fifth for the rocket, a fifth for ground systems, a fifth for the payload, and the rest for various systems work (e.g. integration). If you somehow reduce launch costs to nothing at all, you've introduced the world to the clearly revolutionary potential of four-fifths current cost spaceflight.

So the best we can hope for, even if SpaceX manages to cut the cost of a Falcon 9 launch by 50% (which I doubt) is a 10% savings for the average space project.

And of course, we all know that the airplane analogy (you don't throw away your airplane after each flight) doesn't apply to rockets. Airplanes do not have the same mass fraction, jet engines are vastly more expensive than rocket engines, they are not subjected to the same forces during flight, their purpose is to go from the ground to another point on the ground, and they usually arrive at their destination in one piece. There is no point in comparing rockets to airplanes.

The sheer energy involved in accelerating a payload from 0 km/h to 25000 km/h will always be significant, therefore Space flight will always be expensive. I don't think that kind of energy will ever be routinely available for cheap.

Edited July 11, 2013 by Nibb31

[marach]

If you are recovering your first stage, you don't want an early gravity turn, because any horizontal speed will have to be reversed if you want to return to your launch site. You want a launch profile that remains as vertical as possible until the first stage runs out, so that it can come as straight down as possible, and let the second stage handle most of the horizontal speed. Of course, anyone who has played KSP knows that this is wasteful, and reduces your payload. It also means that you need a beefier second stage, which also eats into the payload mass.

Oooor you place your return point down range X miles and use a chute for initial breaking (cutting it away a second or so before you start your landing burn ofc). You'd still have a smaller max payload due to the fuel you'd want to keep in the first stage for landing but no need for a straight initial climb etc and costs wouldn't be increased that much (especially if the refurb and check point is at the landing site) sure you'd see the first stage turn around go up a little due to having to move it back to the launch site but since it takes time to mate first and second stage anyway the increase wouldn't be astronomical.

[Nibb31]

Parachutes are actually heavy beasts. They can also be complex and are prone to mishaps. A parachute large enough to slow down a Falcon 9 first stage could easily weigh more than the extra fuel needed to brake from terminal velocity to zero.

As for a downrange landing site, the only possibility would be to launch from Texas and to land on a refurbished oil rig somewhere in the Gulf of Mexico, refuel and self-fly the stage back to Texas. That might be feasible, but I think Elon's plan is to return to the launch site for a quick turn around.

Edited July 11, 2013 by Nibb31

[Awaras]

Parachutes are actually heavy beasts. They can also be complex and are prone to mishaps. A parachute large enough to slow down a Falcon 9 first stage could easily weigh more than the extra fuel needed to brake from terminal velocity to zero.

As for a downrange landing site, the only possibility would be to launch from Texas and to land on a refurbished oil rig somewhere in the Gulf of Mexico, refuel and self-fly the stage back to Texas. That might be feasible, but I think Elon's plan is to return to the launch site for a quick turn around.

I remember reading that a SpaceX spokesperson said exactly this - the total weight of the parachutes and other equipment would be greater than the weight of fuel the first stage needs for landing.

[Fuzzy Dunlop]

The landing itself barely uses any fuel at all, its the getting back to base bit that's the drain.

[Bunsen]

But lets not forget that this isn't a holy grail, as Kryten posted this in another thread:

But there's another factor; spaceflight costs involve a heck of a lot more than launch. Satellite operators operate (very roughly) on the 'rule of fifths'; a fifth of the budget for the satellite bus, a fifth for the rocket, a fifth for ground systems, a fifth for the payload, and the rest for various systems work (e.g. integration). If you somehow reduce launch costs to nothing at all, you've introduced the world to the clearly revolutionary potential of four-fifths current cost spaceflight.

So the best we can hope for, even if SpaceX manages to cut the cost of a Falcon 9 launch by 50% (which I doubt) is a 10% savings for the average space project.

But there are feedback effects within that cost structure. Make putting mass in orbit cheap, and the rest of the engineering balance shifts away from custom hyper-optimized designs toward simpler manufacturing, wider design margins, easier analysis, simpler testing, more parts commonality, more mass production, et cetera. Busses get cheaper. Payloads get slightly cheaper. Integration gets cheaper. Ground systems probably don't change much. It will certainly take time for the industry to adapt to those ideas, and some areas will have less to gain than others, but those other "fifths" won't just stay fixed.